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Homework Help: Bright and dark fringes between two slits - waves

  1. Jun 3, 2008 #1
    1. The problem statement, all variables and given/known data
    Explain why we observe bright and dark fringes behind two thin slits illuminated by monochromatic light?

    2. Relevant equationsExplain and justify the mathematical condition that determines whether a dark or bright fringe is formed.

    3. The attempt at a solution
  2. jcsd
  3. Jun 4, 2008 #2
    Google for youngs double slit experiment :)
  4. Jun 4, 2008 #3
    Yep, owls is absolutely right. Here is an interesting link I found
    ( I don't have 15 posts yet thus I can't copy paste the link )
    google for "young's double slit experiment" and click on the second link

    If you still need help on this one, let us know
  5. Jun 4, 2008 #4
    The two slits act as coherent sources of light, and at different points on the screen, the path difference between the two waves falling on that point varies, thus somewhere they interfere constructively (bright point, maxima) and at some points they interfere destructively (minima, dark band).

    lambda / d = x/ L
    d is distance between slits, lambda is the wavelength of monochromatic light, x is distance of first bright fringe from central maxima, L is distance of screen from the slits.
    a bright fringe is obtained where the path difference between the light from the two slits is an integral multiple of lambda. so where
    path diff = n.lamda .. bright fringe is obtained.
    and when path difference is (2n-1).lambda/2 .......a dark band is obtained.
  6. Jun 4, 2008 #5

    Thank you all.
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